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eggshaped
167672.  Thu Apr 19, 2007 6:00 am Reply with quote

Yes, maybe I'm getting confused.

I took it that windspeed has an effect on birds in a similar way to the wind-chill factor, while a convection current does not rely on wind, but rather on the dynamic nature of hot air.

 
dr.bob
167688.  Thu Apr 19, 2007 6:11 am Reply with quote

eggshaped wrote:
Yes, maybe I'm getting confused.


You and me both :)

I like the idea of debunking the "fact" that dark clothes make you hotter, but I'm not entirely convinced by the science involved. For me, basing a debunking question on dodgy science is a dangerous idea.

Mind you, as I've said, I've only got the "executive summary" of the abstract to go on, so there may be something much more meaningful in the actual text of the paper. So I'm entirely prepared to be told I've missed the point entirely, but I'd just like to raise a wee note of caution to make sure this is done right if it's used as a question.

 
Jenny
167967.  Thu Apr 19, 2007 6:19 pm Reply with quote

Couldn't the dark clothes/Bedouin/desert connection be at least partly to do with the absence of water to wash them in? Or is that just me expressing my inner housewife?

 
Gray
168034.  Fri Apr 20, 2007 3:59 am Reply with quote

The problem is that there's a windspeed threshold above which the colour of clothes makes no difference (witness the radiative and convective properties of black vs. white). Below that windspeed, the major factor is the looseness of the clothing, allowing just the convection factor to operate.

Of course, convective chimneys work best when there's a wind blowing across the top, as in the Bernoulli Effect, so the windspeed comes into effect there too.

It's a tricky one, I agree, but I think if we can get the explanation into a concise paragraph, this should work.

 
Flash
168039.  Fri Apr 20, 2007 4:03 am Reply with quote

If you're sitting or lying down (which you would be - it's hot, dammit) then I suppose you wouldn't get the chimney effect in any case?

 
Gray
168055.  Fri Apr 20, 2007 4:23 am Reply with quote

That's true.

I expect the ambient temperature of the air is going to be a large factor as well, which would definitely tip it in black's favour, as it can radiate more efficiently. In the desert the air is extremely hot, whereas in Devon, say, it's not.

 
Albert Terry
708460.  Wed May 12, 2010 5:41 am Reply with quote

I saw the repeat of this episode on Dave last night and spotted what I had previously missed. Stephen actually said:

Quote:
They do wear black. Some people put forward the argument that black might be best, because it's hottest around the bottom, and convection would cause cool air to rise, but no one has really demonstrated that. The fact is, it doesn't really matter what colour you wear, as long as you look cool.

I may have missed something but I was taught that in convection, it is the hot air that rises because it is less dense than cold air. Then again maybe it doesn't - which is perhaps why the weather is always so topsy turvy.

 
SubJunk
816586.  Mon May 16, 2011 4:18 am Reply with quote

I just got around to watching this episode and was surprised to see the claim that this is a false myth.

From California state University at Stanislaus:

Quote:
If you are in the sun and wear black clothing, your clothing will absorb the light (and its energy) and warm up. If you wear white clothing, it will reflect the light rather than absorb it. It will not warm up as fast. White snow reflects most of the light and as a result it warms up more slowly on a sunny day than snow that has dirt or other debris on it that makes its surface darker..


P.S. I hope you don't mind the thread necro. It seemed to have gone unsolved so hopefully this post is welcome.

 
aTao
816690.  Mon May 16, 2011 12:47 pm Reply with quote

One thing that is almost never mentioned in this discussion is that only one side is facing the heat source and black can be a better radiator than white. So what black looses (gains) by adsorbing more heat it gains (looses) by radiating it better.
Best possible solution is light colour facing the heat source, dark colour everywhere else.
Better still reflective foil
Better still, the wall of a pub.

 
hassan el kebir
816712.  Mon May 16, 2011 2:01 pm Reply with quote

When I went out this morning I was wearing a rather fetching brown gallabaya* and I sweated buckets.

When I went out mid-afternoon, by which time it was several blast furnaces worth hotter, I wore a lovely, virginal, white gallabaya* and sweated far fewer buckets.

So, in my experience, white is coolest.....................though, when wearing white, for the sake of modesty, you do need to remember to put a pair of bloomers on before leaving the house.


*in this experiment both gallabayas were pure cotton, no nasty man-made fibres added.

 
48k
1017293.  Mon Aug 19, 2013 11:00 am Reply with quote

The truth is a little simpler.

Bedouin wear black because it is very chilly at night in the desert - around 25 degrees colder than the midday sun.

 
Jenny
1017295.  Mon Aug 19, 2013 11:02 am Reply with quote

Good point 48k - welcome to the forum :-)

 
48k
1017298.  Mon Aug 19, 2013 11:10 am Reply with quote

Thanks :) Just wanted to post that one thing, but maybe I'll get sucked in ... !

 
'yorz
1177595.  Wed Feb 17, 2016 9:25 am Reply with quote

Walk through? He must have been walking in circles for 40 years.

 
Zziggy
1177600.  Wed Feb 17, 2016 9:50 am Reply with quote

Survival in cold deserts too - a problem Santa had to overcome when leading the elves* to their promised workshop.


* I think cousins(?) of our own.

 

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